Various information recording techniques have been developed following the increase in volume of information processing in recent years. Particularly, the areal recording density of HDDs using the magnetic recording technique has been increasing at an annual rate of about 100%. Recently, the information recording capacity exceeding 250 GB has been required per 2.5-inch magnetic disk adapted for use in a HDD or the like. In order to satisfy such a requirement, it is necessary to realize an information recording density exceeding 400 Gbits/inch2. In order to achieve the high recording density in a magnetic disk for use in a HDD or the like, it is necessary to reduce the size of magnetic crystal grains forming a magnetic recording layer serving to record information signals, and further, to reduce the thickness of the layer. However, in the case of conventionally commercialized magnetic disks of the in-plane magnetic recording type (also called the longitudinal magnetic recording type or the horizontal magnetic recording type), as a result of the reduction in size of magnetic crystal grains, there has been the occurrence of a thermal fluctuation phenomenon where the thermal stability of recorded signals is degraded due to superparamagnetism so that the recorded signals are lost. This has been an impeding factor for the increase in recording density of the magnetic disks.
In order to solve this impeding factor, magnetic recording media of the perpendicular magnetic recording type have been proposed in recent years. In the case of the perpendicular magnetic recording type, as is different from the case of the in-plane magnetic recording type, the easy magnetization axis of a magnetic recording layer is adjusted so as to be oriented in a direction perpendicular to the surface of a substrate. As compared with the in-plane magnetic recording type, the perpendicular magnetic recording type can suppress the thermal fluctuation phenomenon and thus is suitable for increasing the recording density. As such a perpendicular magnetic recording medium, there is known a so-called two-layer perpendicular magnetic recording disk comprising, over a substrate, a soft magnetic underlayer made of a soft magnetic substance and a perpendicular magnetic recording layer made of a hard magnetic substance, as is described in, for example, JP-A-2002-74648.
In the meantime, a conventional magnetic disk is provided with a protective layer on a magnetic recording layer formed over a substrate and further with a lubricating layer on the protective layer in order to ensure the durability and reliability of the magnetic disk. Particularly, the lubricating layer used at the outermost surface is required to have various properties such as long-term stability, chemical substance resistance, anti-friction property, and heat resistance.
In order to satisfy such a requirement, perfluoropolyether-based lubricants having hydroxyl groups in molecules have often been used as lubricants for magnetic disks. For example, according to JP-A-862-66417 or the like, there is well known a magnetic recording medium or the like coated with a perfiuoroalkylpolyether lubricant having a structure of HOCH2CF2O(C2F4O)p(CF2O)qCF2CH2OH containing hydroxyl groups at both ends of a molecule. It is known that when hydroxyl groups are present in molecules of a lubricant, the lubricant has excellent adhesion to a protective layer due to the interaction between the protective layer and the hydroxyl groups.